1. Field Of The Invention
The present invention relates to the design of an improved Wien filter for all applications, including use as a velocity filter for identical mass particles or as a mass filter for a beam with a range of particle masses.
2. The Prior Art
Velocity or mass filters using crossed electric and magnetic fields ("Wien filters") are known in the art. Early references, including Herzog, R. (1934) Z. Phys. Vol. 89, p. 447, and Henneberg, W. (1934) Ann. Phys. Vol. 19 (5), p. 335 relate to the use of a Wien filter for acquiring energy spectra of electrons, where the filter is acting as a velocity spectrometer. Ogilvie, K. W., Kittridge, R. J., and Wilkerson, T. D. (1968) Rev. Sci. Instrum. Vol. 39, p. 459 relates to the Wien filter for analysis of heavy particles. Seliger, R. L. (1972) J. Appl. Phys. Vol. 43, p. 2352 considers the Wien filter for use in mass spectrometry.
In all applications, the size of the usable aperture in the mass (velocity) filter is important. Particles passing through currently known Wien filters outside the usable aperture (but still within the physical aperture) will be subject to aberrations which limit the performance attainable with the Wien filter in either the velocity or mass filter operating modes.